How Far is Earth from the Sun? How Far is Earth from the Sun? By Tim Sharp, Reference Editor | September 17, 2012 12:12pm ET MORE The sun is at the heart of the solar system. All of the bodies in the solar system — planets, asteroids, comets, etc. — revolve around it. The distance from Earth to the sun is called an astronomical unit, or AU, which is used to measure distances throughout the solar system. The AU has been defined as 149,597,870,700 meters (92,955,807 miles). Astronomers use the AU for measuring distances throughout the solar system. Jupiter , for example, is 5.2 AU from the sun. Neptune is 30.07 AU from the sun. On the outer edges of the solar system, the Oort Cloud , where comets are thought to originate, is 100,000 AU from the sun. The distance to the nearest star, Proxima Centauri, is about 250,000 AU.

However, to measure longer distances, astronomers use light-years, or the distance that light travels in a single Earth year, which is equal to 63,239 AU. So Proxima Centauri is about 4.2 light-years away. Artists rendering of the Kuiper Belt and Oort Cloud. Credit: NASA Elliptical orbit The AU is the average distance from the Earth to the sun . Earth makes a complete revolution around the sun every 365.25 days ­— one year. However, Earth's orbit is not a perfect circle; it is shaped more like an oval, or an ellipse. Over the course of a year, Earth moves sometimes closer to the sun and sometimes farther away from the sun. Earth's closest approach to the sun, called perihelion, comes in early January and is about 91 million miles (146 million km). The farthest from the sun Earth gets is called aphelion. It comes in early July and is about 94.5 million miles (152 million km). Finding the distance Historically, the first person to measure the distance to the sun was Aristarchus around the year 250 BC.

In more recent times, astronomer Christiaan Huygens calculated the distance from Earth to the sun in 1653. He used the phases of Venus to find the angles in a Venus-Earth-Sun triangle. For example, when Venus appears half illuminated by the sun, the three bodies form a right triangle from Earth's perspective. Guessing (correctly, by chance) the size of Venus, Huygens was able to determine the distance from Venus to Earth, and knowing that distance, plus the angles made by the triangle, he was able to measure the distance to the sun. However, because Huygens' method was partly guesswork and not completely scientifically grounded, he usually doesn't get the credit. In 1672, Giovanni Cassini used a method involving parallax, or angular difference, to find the distance to Mars and at the same time figured out the distance to the sun. He sent a colleague, Jean Richer, to French Guiana while he stayed in Paris. They took measurements of the position of Mars relative to background stars, and triangulated those measurements with the known distance between Paris and French Guiana. Once they had the distance to Mars, they could also calculate the distance to the sun.

Since his methods were more scientific, he usually gets the credit. New equation With the advent of spacecraft and radar, there were now methods for making a direct measure of the distance between the Earth and the sun. The definition of AU had been "the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass, moving with a mean motion of 0.01720209895 radians per day (known as the Gaussian constant)." Along with making things unnecessarily difficult for astronomy professors, that definition actually didn't jibe with general relativity . Using the old definition, the value of AU would change depending on an observer's location in the solar system. If an observer on Jupiter used the old definition to calculate the distance between the Earth and the sun, the measurement would vary from one made on Earth by about 1,000 meters (3,280 feet). Moreover, the Gaussian constant depends on the mass of the sun , and because the sun loses mass as it radiates energy, the value of AU was changing along with it.

The International Astronomical Union voted in August 2012 to change the definition of the astronomical unit to a plain old number: 149,597,870,700 meters. The measurement is based on the speed of light, a fixed distance that has nothing to do with the sun's mass. A meter is defined as the distance traveled by light in a vacuum in 1 / 299,792,458 of a second. — Tim Sharp, Reference Editor Glossary: Astronomical Unit (AU) ASTRONOMICAL UNIT (AU) 1 AU = 149,597,870.700 kilometers (or 149,597,870,700 meters) Definition: An Astronomical Unit is the mean distance between the Earth and the Sun. In 2012, the International Astronomical Union defined the distance to be 149,597,870,700 meters. Historical Background: Tycho Brahe estimated the distance between the Sun and the Earth at 8 million kilometers (5 million miles).

Later, Johannes Kepler estimated the AU was at 24 million kilometers (15 million miles). In 1672, Giovanni Cassini made a much better estimate by using Mars. By observing Mars from Paris and having a colleague, Jean Richer, also observe Mars at the same time in French Guiana in South America, Cassini was able to determine the parallax of Mars. From that Cassini was then able to calculate the distance from Earth to Mars, and then the distance from Earth to the Sun. Cassini calculated the AU to be at 140 million kilometers (87 million miles), which is lower, but very close to the modern day number. Earth's Orbit Around The Sun - Universe Today Universe Today Earth’s Orbit Around The Sun Article Updated: 7 Jan , 2017 by Matt Williams Ever since the 16th century when Nicolaus Copernicus demonstrated that the Earth revolved around in the Sun, scientists have worked tirelessly to understand the relationship in mathematical terms. If this bright celestial body – upon which depends the seasons, the diurnal cycle, and all life on Earth – does not revolve around us, then what exactly is the nature of our orbit around it?

For several centuries, astronomers have applied the scientific method to answer this question, and have determined that the Earth’s orbit around the Sun has many fascinating characteristics. Orbital Characteristics: First of all, the speed of the Earth’s orbit around the Sun is 108,000 km/h, which means that our planet travels 940 million km during a single orbit. The Earth completes one orbit every 365.242199 mean solar days, a fact which goes a long way towards explaining why need an extra calendar day every four years (aka. during a leap year). The planet’s distance from the Sun varies as it orbits. In fact, the Earth is never the same distance from the Sun from day to day. When the Earth is closest to the Sun, it is said to be at perihelion. This occurs around January 3rd each year, when the Earth is at a distance of about 147,098,074 km. The average distance of the Earth from the Sun is about 149.6 million km, which is also referred to as one astronomical unit (AU).

When it is at its farthest distance from the Sun, Earth is said to be at aphelion – which happens around July 4th where the Earth reaches a distance of about 152,097,701 km. And those of you in the northern hemisphere will notice that “warm” or “cold” weather does not coincide with how close the Earth is to the Sun. That is determined by axial tilt (see below). Elliptical Orbit: Next, there is the nature of the Earth’s orbit. Rather than being a perfect circle, the Earth moves around the Sun in an extended circular or oval pattern. This is what is known as an “elliptical” orbit. This orbital pattern was first described by Johannes Kepler, a German mathematician and astronomer, in his seminal work Astronomia nova (New Astronomy). An illustration of Kepler’s three laws of motion, which show two planets that have elliptical orbits around the Sun. Credit: Wikipedia/Hankwang After measuring the orbits of the Earth and Mars, he noticed that at times, the orbits of both planets appeared to be speeding up or slowing down.

This coincided directly with the planets’ aphelion and perihelion, meaning that the planets’ distance from the Sun bore a direct relationship to the speed of their orbits. It also meant that both Earth and Mars did not orbit the Sun in perfectly circular patterns. In describing the nature of elliptical orbits, scientists use a factor known as “eccentricity”, which is expressed in the form of a number between zero and one. If a planet’s eccentricity is close to zero, then the ellipse is nearly a circle. If it is close to one, the ellipse is long and slender. Earth’s orbit has an eccentricity of less than 0.02, which means that it is very close to being circular. That is why the difference between the Earth’s distance from the Sun at perihelion and aphelion is very little – less than 5 million km. Seasonal Change: Third, there is the role Earth’s orbit plays in the seasons, which we referred to above.

The four seasons are determined by the fact that the Earth is tilted 23.4° on its vertical axis, which is referred to as “axial tilt.” This quirk in our orbit determines the solstices – the point in the orbit of maximum axial tilt toward or away from the Sun – and the equinoxes, when the direction of the tilt and the direction to the Sun are perpendicular. Over the course of a year the orientation of the axis remains fixed in space, producing changes in the distribution of solar radiation. Credit: NOAA/Thomas G. Andrews In short, when the northern hemisphere is tilted away from the Sun, it experiences winter while the southern hemisphere experiences summer. Six months later, when the northern hemisphere is tilted towards the Sun, the seasonal order is reversed. In the northern hemisphere, winter solstice occurs around December 21st, summer solstice is near June 21st, spring equinox is around March 20th and autumnal equinox is about September 23rd. The axial tilt in the southern hemisphere is exactly the opposite of the direction in the northern hemisphere. Thus the seasonal effects in the south are reversed.

While it is true that Earth does have a perihelion, or point at which it is closest to the sun, and an aphelion, its farthest point from the Sun, the difference between these distances is too minimal to have any significant impact on the Earth’s seasons and climate. Lagrange Points: Another interesting characteristic of the Earth’s orbit around the Sun has to do with Lagrange Points . These are the five positions in Earth’s orbital configuration around the Sun where where the combined gravitational pull of the Earth and the Sun provides precisely the centripetal force required to orbit with them. Sun-Earth Lagrange Points. Credit: Xander89/Wikimedia Commons The five Lagrange Points between the Earth are labelled (somewhat unimaginatively) L1 to L5. L1, L2, and L3 sit along a straight line that goes through the Earth and Sun. L1 sits between them, L3 is on the opposite side of the Sun from the Earth, and L2 is on the opposite side of the Earth from L1. These three Lagrange points are unstable, which means that a satellite placed at any one of them will move off course if disturbed in the slightest.

The L4 and L5 points lie at the tips of the two equilateral triangles where the Sun and Earth constitute the two lower points. These points liem along along Earth’s orbit, with L4 60° behind it and L5 60° ahead. These two Lagrange Points are stable, hence why they are popular destinations for satellites and space telescopes. The study of Earth’s orbit around the Sun has taught scientists much about other planets as well. Knowing where a planet sits in relation to its parent star, its orbital period, its axial tilt, and a host of other factors are all central to determining whether or not life may exist on one, and whether or not human beings could one day live there. We have written many interesting articles about the Earth’s orbit here at Universe Today. Here’s 10 Interesting Facts About Earth , How Far is Earth from the Sun? , What is the Rotation of the Earth? , Why are there Seasons? , and What is Earth’s Axial Tilt? For more information, check out this article on NASA- Window’s to the Universe article on elliptical orbits or check out NASA’s Earth: Overview . Astronomy Cast also espidoes that are relevant to the subject.

Here’s BQuestions Show: Black black holes, Unbalancing the Earth, and Space Pollution . Sources: Distances to the Sun and Stars Distances to the Sun and Stars Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay First-time Visitors: Please visit Site Map and Disclaimer . Use "Back" to return here. It is no accident that we call enormous numbers "astronomical". Astronomers deal with quantities so vast, distance, mass, and energy, that they tax our imaginations and mathematical skills. But such vast quantities also provide some of the most exciting ideas the human mind can encounter. Distances In The Solar System We can determine the distances to objects in the Solar System, and to nearby stars, by Triangulation. If we observe an object from two stations a known distance apart, we can find the distance to the object. For objects in the Solar System, we can measure the position of a the object from different sides of the Earth. Observations of Venus crossing or transiting the face of the Sun, or asteroids passing very close to the Earth, were once used. Once we know the actual distance of any object, Kepler's Third Law allows us to determine the distances of every object in the Solar System.

[Nowadays we can actually bounce radar signals off nearby planets and measure the distance more accurately this way] Distances To Nearby Stars The stars are so far away that they look the same all over the Earth. The farthest apart we can ever make observations at present is from opposite sides of the Earth's orbit, on opposite sides of an ellipse 186 million miles in diameter. When we photograph the stars six months apart, some of them shift very slightly because of the Earth's motion. You can demonstrate this shift, or parallax, easily. Hold up your finger at arm's length and alternately open and close each eye. Your finger will appear to move relative to objects in the background. For the stars, the parallactic shift is extremely tiny but it can be measured. The distances to the stars turn out to be so great that we need a new unit of distance: the light year . The light year is not a unit of time; it is the distance light travels in a year, or about 6 trillion miles (10 trillion km) Measuring parallax involves measuring very tiny angles. A degree can be divided into 60 minutes and each minute into 60 seconds.

A quarter spans one degree at a distance of 1.5 meters. The Sun and Moon span about half a degree in the sky. A quarter spans one minute at a distance 60 times greater, or 90 meters. Venus at its nearest and Jupiter both span about a minute of arc in the sky. A quarter spans one second at a distance of 5 kilometers. The moons of Jupiter appear about one second of arc across. Astronomers routinely measure the positions of objects to about 0.1 second of arc and the Hubble Space Telescope, above the distortions produced by Earth's atmosphere, can see details that span a few hundredths of a second of arc. Astronomers also use another distance term, the parsec. A parsec is the distance at which a star would have a parallax of one second of arc, or 3.26 light years. Parsecs are convenient because the distance in parsecs is simply one over the parallax, making it easy to convert the two units. Hipparcos Hipparcos of Nicaea lived in the second century B.C. and left us the first star catalog.

On August 8, 1989, a satellite named in his honor, the High Precision Parallax Collecting Satellite, was launched by the European Space Agency. Despite an engine malfunction that left the satellite in a less desirable orbit than planned, the spacecraft gathered data on stellar positions and magnitudes until March 1993. The data were processed and finally released in catalog form in the summer of 1997. The data are of unprecedented accuracy and have completely revolutionized the determination of stellar distances. Hipparcos worked by observing stars through two telescopes aimed 58 degrees apart. The light from the two telescopes was merged into a detector with a fine grid of wires. As the satellite rotated, different stars passed through the field of view of each telescope and blinked on and off as the stars passed across the grid of wires. These observations allowed extremely accurate relative positions of the stars to be determined. The relative positions of all the stars could then be combined into an extremely accurate catalog of star positions across the entire sky. For 118,000 selected stars, Hipparcos measured their parallax accurate to .001 second of arc.

That's the apparent diameter of a quarter at a distance of 5000 kilometers, or putting a quarter in New York and viewing it from San Francisco. It's also the amount the hair on a person a meter away appears to grow in one second. A secondary mission named Tycho measured another million stars to an accuracy of "only" 0.01 second. How Accurate Are Stellar Distances? Earth-Based Measurements Distances in older star catalogs look so authoritative that many people think the distances to the stars are known very exactly, but this is not true. For parallax measurements made from Earth: The nearest star is some 4.2 light years away, and that distance was known to within an accuracy of better than 0.1 light year. For a star measured as 20 light years away, the distance estimate is accurate to within a light year or so. For stars 50 light years away, the margin of error is perhaps 5 to 10 light years. Beyond 100 light years, the parallax is so tiny it cannot be measured accurately, and astronomers resort to more indirect methods to find the distances to the stars. We will examine some of these methods later.

Hipparcos Measurements The Hipparcos catalog of star distances has made older distance estimates obsolete and all new astronomical publications will use the Hipparcos figures. Even more accurate observational systems are in the planning stages. However, until there is a distance measuring spacecraft on continuous duty, capable of being aimed at new targets on demand, there will still be earth-based parallax measurements and these will be subject to the same limitations as the older measurements The following table shows how Hipparcos has improved our knowledge of stellar distances: Accuracy Level 28,000 stars 300 light years The earth-based data are approximate. Much of the improvement in Hipparcos is due to its being completely automatic, whereas earth-based data were combined by laborious measurements of individual stars. Thus, earth-based data were incomplete and of variable accuracy. Travel Times to the Stars Films like Star Wars create the impression that travelling from star to star is only a bit more complex than driving down to the corner store for a loaf of bread. In fact, distances in the Universe are so vast it is hard to comprehend them. Everyday speeds will not begin to cover the distances in the Universe.

For example, walking nonstop at a brisk pace, a person could cover about 75 miles (120 km) in a 24-hour day. If he or she could keep up the pace indefinitely, it would take about 40 days to cross the 3000-mile (5000 km) width of the United States, and about 11 months to travel the 25,000 (40,000 km) miles around the Earth. It would take about 8 1/2 years to travel the 235,000 miles (380,000 km) to the Moon, and 95 years to cover the distance to Venus at its closest. In an automobile travelling a steady 55 miles (90 km) per hour, it takes about 2 1/2 days to cross the United States and about 19 days to circle the Earth. It will still take six months to travel the distance to the Moon. Venus, however, is 100 times farther away at its closest, and would be a 54-year trip. We are not even out of the inner Solar System yet.

At 55 miles an hour, just under half a million miles (800,000 km) a year, the Sun is two centuries away. If we had started out from the Sun at that speed in 1 A.D. we would now have covered about 960 million miles (1.54 billion km) and would be just beyond Saturn, only a third of the way out of the Solar System. In a jetliner, at 550 miles (900 km) an hour, we cover distance 10 times as fast as in a car. The United States is 5-1/2 hours wide, and two days will take us around the world. The Moon is three weeks away, Venus over 5 years, the Sun 20. Pluto, the outermost planet, is still 750 years away. The nearest star is still so far away as to be unimaginable: 52 million years. At 18,000 miles (29,000 km) an hour, the Space Shuttle crosses the Unites States in 10 minutes and circles the Earth in an hour and a half.

In 13 hours it covers the distance to the Moon, but even so would take two months to cover the distance to Venus and seven to cover the distance to the Sun. Pluto is still over two years away. The nearest star is still 160,000 years away. Light, at 186,300 miles (298,000 km) per second, could circle the Earth seven times in one second and reach the Moon in 1-1/2 seconds. The Sun is about 8-1/2 minutes away at the speed of light. It takes light about 5-1/2 hours to reach Pluto from the Sun, but 4.3 years to reach the next star. % Scale Models of the Universe It is impossible to make a physical model that shows Man, the planets, and the stars on the same scale. If we make the Earth a quarter (one inch or 2.5 cm in diameter), the Moon becomes a pea 29 inches (74 cm) away. The Sun is 9 feet (2.7 m) across and 1000 feet (300 m) away.

Pluto is 7 miles (11 km) away, and the nearest star is still off the real Earth: 49,000 miles (79,000 km) away. If we let the Sun be a quarter, the Earth is a speck 1/100 inch (1/40 cm) in diameter and ten feet (3 m) away. Pluto is more than a football field away: 350 feet (110 m). And at last we can begin to show stars in our scale model. The nearest one is about 500 miles (900 km) away, and it, too, is the size of a quarter, with a pea-sized companion star about 200 feet (60 m) away. Placing a single coin in each State capital covers the U.S. with coins more densely than space is filled with stars. Beyond The Nearest Stars Most of the stars we see with the naked eye at night are within a few hundred light years. A few are as far away as 2000 light years, only about 1/50 the diameter of our Galaxy.

We can only use parallax to determine the distances of stars within about 50 light years, a realm that bears about the same relationship to our Galaxy as a period bears to the size of this page. How can astronomers measure the distances of distant stars? The City Lights Analogy There are many ways to explain how we know the arrangement of the universe, but perhaps the clearest analogy is the City Lights Analogy. Imagine being on the roof of a tall building with no way to leave. At night you can see lights in all directions. How can you map your "universe"? For nearby lights, you can use triangulation. By observing from different locations on the roof, and measuring changes in the relative positions of the lights, you can determine how far away the lights are. Once you know how far away the lights are, you can determine their true brightness. In nearby towns, the lights are all too far away to measure their distances by triangulation, but you can recognize lights of the same types as those you see nearby. Since you know how bright these nearby lights are, you can calculate how far off the lights in the town are.

For distant towns, you cannot even see individual lights, but you know how far away the nearby towns are, and how much total light the towns emit, so you can use this information to estimate how far the distant towns are. At even greater distances, only clusters of towns are visible, and finally only great urban complexes, but at each stage you can use what you already know to discaover facts about the more distant universe. We build our picture of the Universe in much the same way. Spectroscopic Distances Within the range we can measure parallax accurately, there are thousands of stars of many spectral types. With the apparent brightness and distances of these stars known, it is possible to determine their absolute magnitudes. Distant stars of the same spectral types will probably have the same absolute magnitudes, enabling us to estimate the distance to the unknown star. For isolated stars, this is virtually the only method of determining distance. When we say that the bright star Deneb is 1600 light years away, for example, the distance is an estimate based on its brightness and spectral type. The distance could easily be 25% larger or smaller. Deneb is still too far away for even Hipparcos to measure accurately.

The Cluster Method Another technique for finding the distances of faraway stars involves star clusters. On photographs of clusters taken many years apart, the stars move. Some stars will move at higher speeds than others, but the velocity will show a characteristic statistical pattern. We can also measure the Doppler shift of stars in the cluster to find out how fast the stars are moving toward or away from us. The star cluster has no connection to Earth at all, so the velocity pattern of stars along our line of sight should be the same as that across our line of sight. Radial velocity can be determined in kilometers per second. By assuming the range of velocities across our line of sight is the same, we can determine what angle in the sky corresponds to a known distance and thus determine the distance to the cluster. Cepheid Variables The cluster method works out to a thousand light years or so. Fortunately, within that distance are stars that give us a yardstick to distant galaxies. These are the Cepheid Variables. Cepheids are named for a star in the constellation Cepheus, the first star of this type discovered, but the most famous Cepheid, and also the nearest, is Polaris, the Pole Star.

Polaris is about 300 light years away and varies in brightness too slightly to be obvious to the unaided eye. Before Hipparcos, the distance to Cepheids had to be determined indirectly by the cluster method, but now the distances to several have been determined directly. Cepheid variables are yellow-white giant stars that pulsate and vary in brightness, but in a regular way. The brighter the absolute magnitude of a Cepheid, the faster it pulsates. It is easy to measure the period of a Cepheid variable, and armed with this information, we can determine the absolute brightness of the star. Instead of using distance and apparent magnitude to find absolute magnitude, we compare the absolute and apparent brightness of the star to determine its distance. How do you measure the distance between Earth and the Sun? (Intermediate) - Curious About Astronomy? Ask an Astronomer How do you measure the distance between Earth and the Sun?

(Intermediate) (Intermediate) >" onclick="window.open(this.href,'win2','status=no,toolbar=no,scrollbars=yes,titlebar=no,menubar=no,resizable=yes,width=640,height=480,directories=no,location=no'); return false;" rel="nofollow"> How do astronomers calculate the distance of the Sun from the Earth, or the actual size of the Sun, or the speed of travel of Earth in its orbit around the Sun? Clearly, from an answer to one of these questions one can find out the answers to the others. But how do we find the first answer? Short version: What we actually measure is the distance from the Earth to some other body, such as Venus. Then we use what we know about the relations between interplanetary distances to scale that to the Earth-Sun distance. Since 1961 , we have been able to use radar to measure interplanetary distances - we transmit a radar signal at another planet (or moon or asteroid ) and measure how long it takes for the radar echo to return. Before radar, astronomers had to rely on other (less direct) geometric methods .

In more detail: The first step in measuring the distance between the Earth and the Sun is to find the relative distances between Earth and other planets. (For instance, what is the ratio of the Jupiter-Sun distance to the Earth-Sun distance?) So, let us say that the distance between Earth and the Sun is "a". Now, consider the orbit of Venus. To a first approximation, the orbits of Earth and Venus are perfect circles around the Sun, and the orbits are in the same plane. Take a look at the diagram below (not to scale). From the representation of the orbit of Venus, it is clear that there are two places where the Sun-Venus-Earth angle is 90 degrees. At these points, the line joining Earth and Venus will be a tangent to the orbit of Venus. These two points indicate the greatest elongation of Venus and are the farthest from the Sun that Venus can appear in the sky.

(More formally, these are the two points at which the angular separation between Venus and the Sun, as seen from Earth, reaches its maximum possible value.) Another way to understand this is to look at the motion of Venus in the sky relative to the Sun: as Venus orbits the Sun, it gets further away from the Sun in the sky, reaches a maximum apparent separation from the Sun (corresponding to the greatest elongation), and then starts going towards the Sun again. This, by the way, is the reason why Venus is never visible in the evening sky for more than about three hours after sunset or in the morning sky more than three hours before sunrise. Now, by making a series of observations of Venus in the sky, one can determine the point of greatest elongation. One can also measure the angle between the Sun and Venus in the sky at the point of greatest elongation. In the diagram, this angle will be the Sun-Earth-Venus angle marked as "e" in the right angled triangle.

Now, using trigonometry, one can determine the distance between Earth and Venus in terms of the Earth-Sun distance: (distance between Earth and Venus) = a × cos(e) Similarly, with a little more trigonometry: (distance between Venus and the Sun) = a × sin(e) The greatest elongation of Venus is about 46 degrees, so by this reasoning, the Sun-Venus distance is about 72% of the Sun-Earth distance. Similar observations and calculations yield the relative distance between the Sun and Mercury. (However, Mars and the outer planets are more complicated.) Historically, the first known person to use geometry to estimate the Earth-Sun distance was Aristarchus (c. 310-230 BC), in ancient Greece. He measured the angular separation of the Sun and the Moon when the Moon was half-illuminated to derive the distance between Earth and Sun in terms of the distance between the Earth and the Moon. His reasoning was correct, but his measurements were not. Aristarchus calculated that the Sun is about nineteen times farther than the Moon; it is actually about 390 times farther than the Moon.

Another ancient Greek astronomer, Eratosthenes (276-194 BC), estimated the distance between Earth and Sun to be either 4,080,000 stadia or 804,000,000 stadia . There is disagreement regarding the correct translation of Eratosthenes' value, and further disagreement over which length of a stadium was used by Eratosthenes. Various sources estimate that the length of a stadium (also called a stadion or stade), converted to modern units, is between 157 meters and 209 meters. Then 4,080,000 stades is less than 1% of the actual Earth-Sun distance, no matter which definition of a stade one chooses. However, 804,000,000 stadia is between 126 million and 168 million kilometers - a range which includes the actual Earth-Sun distance of (approximately) 150 million kilometers. So Eratosthenes may have found a fairly accurate value for the Earth-Sun distance (possibly with some luck), but we can't say for sure.

The first rigorous and accurate scientific measurement of the Earth-Sun distance was made by Cassini in 1672 by parallax measurements of Mars. He and another astronomer observed Mars from two places simultaneously. A century later, a series of observations of transits of Venus provided an even better estimate. Since 1961 , the distance to Venus can be determined directly, by radar measurements, where a series of radio waves is transmitted from Earth and is received after it bounces off Venus and comes back to Earth. By measuring the time taken for the radar echo to come back, the distance can be calculated, since radio waves travel at the speed of light. Once this Earth-Venus distance is known, the distance between Earth and the Sun can be calculated. As you have indicated, once the distance between Earth and Sun is known, one can calculate all the other parameters. We know that the Sun, as seen from Earth, has an angular diameter of about 0.5 degrees. Again, using trigonometry, the radius or diameter of the Sun can be calculated from the distance between Earth and Sun, a, as 2×Rsun = tan(0.5 degrees) × a.

Also, since we know the time taken by the Earth to go once around the Sun (P = 1 year), and the distance traveled by the Earth in this process (approximately 2πa, since Earth's orbit is nearly circular), we can calculate the average orbital speed of Earth as v = (2πa)/P. Anyway, the relevant numbers are: Earth-Sun distance, a = roughly 150 million km, defined as one Astronomical Unit ( AU ) Radius of the Sun, Rsun = roughly 700,000 km Orbital speed of Earth, v = roughly 30 km/s References: Jagadheep D. Pandian Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy . These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow.

Jagadheep is currently at the Indian Institute of Space Scence and Technology. Similar Questions that might Interest You... Sun | Define Sun at Dictionary.com sun noun 1. (often initial capital letter) the star that is the central body of the solar system, around which the planets revolve and from which they receive light and heat: its mean distance from the earth is about 93 million miles (150 million km), its diameter about 864,000 miles (1.4 million km), and its mass about 330,000 times that of the earth; its period of surface rotation is about 26 days at its equator but longer at higher latitudes. 2. the sun considered with reference to its position in the sky, its visibility, the season of the year, the time at which or the place where it is seen, etc. 3. a self-luminous heavenly body; star. 4. sunshine; the heat and light from the sun: to be exposed to the sun. 5. a figure or representation of the sun, as a heraldic bearing usually surrounded with rays and marked with the features of a human face. 6.

something likened to the sun in brightness, splendor, etc. 7. They traveled hard from sun to sun. 9. verb (used with object), sunned, sunning. 10. to expose to the sun's rays. 11. to warm, dry, etc., in the sunshine. 12. to put, bring, make, etc., by exposure to the sun. verb (used without object), sunned, sunning. 13. to be exposed to the rays of the sun: to sun in the yard. Idioms against the sun, Nautical. counterclockwise. 15. place in the sun, a favorable or advantageous position; prominence; recognition: The new generation of writers has achieved a place in the sun. 16. under the sun, on earth; anywhere: the most beautiful city under the sun. 17. with the sun, Nautical. clockwise.

Origin of sun Old English 900 before 900; Middle English sun, sonne, Old English sunne; cognate with German Sonne, Old Norse sunna, Gothic sunno; akin to Old Norse sōl, Gothic sauil, Latin sōl (see solar 1), Greek hḗlios (see helio- ), Welsh haul, Lithuanian saũlė, Polish słońce Related forms Examples from the Web for sun Expand Contemporary Examples With the sun entering Libra, squaring Pluto, you are being asked to take a stand for something, gosh-darn-it. Behind CBS' Morning Show Shakeup Howard Kurtz November 29, 2010 The sun was setting, and he pointed to a cobweb glistening in a ray of light. A Jolly Fellowship Frank R. Stockton It was still dark, for the sun rises and sets at six o'clock on the equator. In Africa John T. McCutcheon British Dictionary definitions for sun Expand noun 1. the star at the centre of our solar system.

It is a gaseous body having a highly compressed core, in which energy is generated by thermonuclear reactions (at about 15 million kelvins), surrounded by less dense radiative and convective zones serving to transport the energy to the surface (the photosphere). The atmospheric layers (the chromosphere and corona) are normally invisible except during a total eclipse. Mass and diameter: 333 000 and 109 times that of earth respectively; mean distance from earth: 149.6 million km (1 astronomical unit) related adjective solar 2. any star around which a planetary system revolves 3. the sun as it appears at a particular time or place: the winter sun 4. the radiant energy, esp heat and light, received from the sun; sunshine 5. a person or thing considered as a source of radiant warmth, glory, etc 6. a pictorial representation of the sun, often depicted with a human face 7. (poetic) a year or a day 8. (archaic) sunrise or sunset (esp in the phrase from sun to sun) 10. catch the sun, to become slightly sunburnt 11.

place in the sun, a prominent or favourable position 12. (nautical) shoot the sun, take the sun, to measure the altitude of the sun in order to determine latitude 13. touch of the sun, slight sunstroke 14. under the sun, beneath the sun, on earth; at all: nobody under the sun eats more than you do verb suns, sunning, sunned to expose (oneself) to the sunshine 16. (transitive) to expose to the sunshine in order to warm, tan, etc Derived Forms Old English sunne; related to Old High German sunna, Old Frisian senne, Gothic sunno Sun. Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for sun Expand n. Old English sunne, from Proto-Germanic *sunnon (cf.

Old Norse, Old Saxon, Old High German sunna, Middle Dutch sonne, Dutch zon, German Sonne, Gothic sunno), from PIE *s(u)wen- (cf. Avestan xueng "sun," Old Irish fur-sunnud "lighting up"), alternative form of root *saewel- "to shine, sun" (see Sol ). Old English sunne was fem., and the fem. pronoun was used until 16c.; since then masc. has prevailed. The empire on which the sun never sets (1630) originally was the Spanish, later the British. To have one's place in the sun (1680s) is from Pascal's "Pensées"; the German imperial foreign policy sense (1897) is from a speech by von Bülow. v. 1510s, "to set something in the sun," from sun (n.). Meaning "to expose oneself to the sun" is recorded from c.1600. Sun-bathing is attested from c.1600. Online Etymology Dictionary, © 2010 Douglas Harper sun (sŭn) Often Sun.

A medium-sized, main-sequence star located in a spiral arm of the Milky Way galaxy, orbited by all of the planets and other bodies in our solar system and supplying the heat and light that sustain life on Earth. Its diameter is approximately 1.4 million km (868,000 mi), and its mass, about 330,000 times that of Earth, comprises more than 99 percent of the matter in the solar system. It has a temperature of some 16 million degrees C (27 million degrees F) at its core, where nuclear fusion produces tremendous amounts of energy, mainly through the series of reactions known as the proton-proton chain. The energy generated in the core radiates through a radiation zone to an opaque convection zone, where it rises to the surface through convection currents of the Sun's plasma. The Sun's surface temperature (at its photosphere) is approximately 6,200 degrees C (11,200 degrees F). Turbulent surface phenomena analogous to the Earth's weather are prevalent, including magnetic storms, sunspots, and solar flares.

The Sun was formed along with the rest of the solar system about 4.5 billion years ago and is expected to run out of its current hydrogen fuel in another 5 billion years, at which point it will develop into a red giant and ultimately into a white dwarf. See Table at solar system . See Note at dwarf star . The American Heritage® Science Dictionary Copyright © 2002. Published by Houghton Mifflin. All rights reserved. The American Heritage® Abbreviations Dictionary, Third Edition Copyright © 2005 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. sun in the Bible Expand (Heb. shemesh), first mentioned along with the moon as the two great luminaries of heaven (Gen. 1:14-18). By their motions and influence they were intended to mark and divide times and seasons. The worship of the sun was one of the oldest forms of false religion (Job 31:26,27), and was common among the Egyptians and Chaldeans and other pagan nations. The Jews were warned against this form of idolatry (Deut.

4:19; 17:3; comp. 2 Kings 23:11; Jer. 19:13). Easton's 1897 Bible Dictionary Idioms and Phrases with sun Expand Cool Cosmos Distance Measure In astronomy, the most commonly used measures of distance are the light year, parsec and astronomical unit. Astronomical Unit (A.U.) An astronomical unit (A.U.) is the average distance between the Earth and the Sun, which is about 93 million miles or 150 million kilometers. Astronomical units are usually used to measure distances within our solar system. For example, the planet Mercury is about 1/3 of an A.U. from the Sun, while the farthest planet, Pluto, is about 40 A.U. from the Sun (thats 40 times as far away from the Sun as the Earth is). Light-Year (ly) Most objects in space are so far away, that using a relatively small unit of distance, such as an astronomical unit, is not practical. Instead, astronomers measure distances to objects which are outside our solar system in light-years.

A light-year (ly) is the distance that light can travel in one year in a vacuum (empty space). The speed of light is about 186,000 miles or 300,000 kilometers per second. So, in one year light travels a distance of about 5,880,000,000,000 miles or 9,460,000,000,000 kilometers or 63,240 A.U.. This distance is 1 light-year. For example, the nearest star to us is about 4.3 light-years away. Our galaxy, the Milky Way, is about 150,000 light-years across, and the nearest large galaxy, Andromeda, is 2.3 million light-years away. Parsec (pc) Astronomers use another unit of distance called a parsec (pc), which is equal to 3.26 light-years. The definition of the parsec is based on a triangle.

A parsec is the length of the long leg of a right triangle, whose short leg is one astronomical unit when the angle between the Sun and the Earth, as seen from an object in space (a star for example), is one arcsecond The word parsec stands for "parallax of one arc second" One kiloparsec (kpc), is one thousand parsecs. One megaparsec (Mpc) is one million parsecs. SUMMARY

Question: What term is used for the distance from the earth to the sun?
Answer: Astronomical Unit